Process for de-selenizing copper

ABSTRACT

Molten copper containing selenium is treated with an alkali metal sulfide, added as such or formed in situ by the addition of an alkali metal sulfate and a carbonaceous reducing agent, and a refining matte phase layer containing an alkali metal sulfide as refining agent is formed on the molten copper surface as a result of the treatment. The matte phase layer is retained on the molten copper surface for a period sufficient to enable passage of the selenium into the matte phase layer in amount sufficient to reduce the selenium content of the copper to a desired value. The selenium in the matte phase layer is thereafter separated from the molten copper, for instance by skimming off the matte phase layer.

Larson Nov. 13, 1973 PROCESS FOR DE-SELENIZING COPPER Harold R. Larson, North Plainfield, NJ.

American Smelting and Refining Company, New York, NY.

Filed: Dec. 14, 1971 Appl. No.: 207,868

Inventor:

[73] Assignee:

U.S. Cl 75/93 AD, 75/76 Int. Cl C22b 9/10 Field of Search 75/76, 72-75,

[56] References Cited UNITED STATES PATENTS Primary Examiner-L. Dewayne Rutledge Assistant ExaminerM. J. Andrews AttorneyElwood J. Schaffer et al.

[5 7] ABSTRACT Molten copper containing selenium is treated with an alkali metal sulfide, added as such or formed in situ by the addition of an alkali metal sulfate and a carbonaceous reducing agent, and a refining matte phase layer containing an alkali metal sulfide as refining agent is formed on the molten copper surface as a result of the treatment. The matte phase layer is retained on the molten copper surface for a period sufficient to enable passage of the selenium into the matte phase layer in amount sufficient to reduce the selenium content of the copper to a desired value. The selenium in the matte phase layer is thereafter separated from the molten copper, for instance by skimming off the matte phase layer.

35 Claims, 2 Drawing Figures CHARGE 10 POURING SPOUT PROCESS FOR DE-SELENIZING COPPER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to de-selenizing copper and more especially to a new and improved process for the removal of selenium from molten copper.

2. Description of the Prior Art The presence of selenium as an impurity in refined copper is known to have an adverse affect on the properties of the copper. Specifically selenium adversely affects the annealability of the copper, and this adverse affect is disadvantageous to modern copper fabricating plants inasmuch as the annealability capability of the copper is usually of special importance to the fabricating plants. Further, the presence of significant quantities of selenium in anode copper at times create serious refining difficulties, with the selenium being transferred from anode to cathode during electro-refining resulting in poorer quality cathode copper. Although the exact mechanism of selenium transfer from anode to cathode is not entirely understood, it is believed to probably involve the mechanical transfer of discrete slime particles containing the selenium to the cathode surface and their encapsulation by the copper as the cathode grows.

US. Pat. No. 1,945,074 discloses the recovery of selenium from molten blister copper or the molten product of a converting operation between the stages of white metal and blister copper. The molten metal is subjected to the action of a refining slag containing one or more alkali metal compounds, such as alkali metal oxides, or other suitable compounds of alkali metals such as sodium and potassium, or the molten copper may be treated with an alkali metal such as, for example, metallic sodium in the presence of sufficient nonmetallic oxides to form a slag with the resulting sodium oxide, sodium sulfide and sodium selenide. The slagcovered molten metal is agitated and subjected to the action of a reducing agent, such as oil, reducing gas, powdered coal or coke, and the agitation is continued until the sulfur and selenium are substantially completely eliminated from the molten copper with the selenium reporting in the slag. In the method of US. Pat. No. 1,945,074 the refining slag layer is an oxide slag containing alkali metal oxides as refining agent and sodium sulfide is present in such oxide refining slag in a small, insignificant or inconsequential amount as an impurity only and not as a purifying or refining agent. The oxide refining slag of US. Pat. No. 1,945,074 also con tains copper oxides and a very small amount of copper sulfide relative to the copper oxides. This oxide refining slag of US. Pat. No. 1,945,074 is contrasted with the refining matte phase layer of the present invention which contains essentially the alkali metal sulfide as refining agent and with the alkali metal sulfide usually present in the matte phase layer in a major amount. The refining matte phase layer of this invention, which is a sulfide matte phase layer, also contains copper sulfide and a small amount of copper oxides relative to the copper sulfide and alkali metal sulfide. A small amount of alkali metal oxides are also present as an inconsequential dilutant in the refining matte phase layer of the present invention. Although such small, inconsequential amounts of the alkali metal oxides cause no serious difficulty to the process of this invention as long as their level is low, the presence of larger amounts of the alkali metal oxides are disadvantageous due to lowering the ing larger quantities of reagents and as such considerably greater difficulty and expense. Further the reagents used in the method of U.S. Pat. No. 1,945,074 are more corrosive to the furnace refractories than are the reagents of the present invention.

BRIEF SUMMARY OF THE INVENTION The process for de-selenizing molten copper in accordance with this invention comprises:

a. treating the molten copper containing selenium with an alkali metal sulfide;

b. forming a refining matte phase containing the alkali metal sulfide as refining agent in contact with the molten copper as a result of the aforesaid alkali metal sulfide treatment;

c. maintaining the refining matte phase in contact with the selenium-containing molten copper for a period sufficient to enable passage of a sufficient amount of selenium into the matte phase to reduce the selenium content of the copper to a desired lower level or value; and

d. separating the selenium in the refining matte phase from the de-selenized molten copper, i.e. copper of reduced selenium content, while such matte phase is on the molten copper surface as a refining matte phase layer.

In the de-selenizing process herein, the refining matte phase containing the alkali metal sulfide is usually formed as a layer on the molten copper surface, and this refining matte phase layer is usually retained on the molten copper surface in contact with the molten copper for a time sufficient to enable passage of a sufficient amount of selenium into the matte phase layer to reduce the selenium content of the copper to a desired value. The selenium in the refining matte phase layer is then separated from the molten copper, usually by skimming the matte phase layer from the molten copper surface.

The alkali metal sulfide utilized to treat the molten copper is added to the molten copper as the alkali metal sulfide per se, or is formed in situ by the addition to the molten copper and the reaction thereon and/or therein of an alkali metal sulfate and a carbonaceous reducing agent, for example coke.

The selenium content of the copper has been consistently reduced from levels materially above 0.15 percent selenium down to a low level or value below 0.15 percent selenium and even below 0.01 percent selenium.

So far as I am aware, any copper containing selenium can be de-selenized in accordance with this invention while in the molten state. This invention is especially well suited for de-selenizing blister copper. In the case of blister copper, it is not necessary to pole the copper prior to de-selenizing by this invention. However, if desired, the copper may be poled to reduce its oxygen content prior to the de-selenizing. Copper matte is not copper as such but sulfides of copper and iron, and cannot be de-selenizedby this invention.

The refining matte phase and the refining matte phase layer of this invention contains the alkali metal sulfide, e.g. sodium sulfide, as refining agent, copper sulfides and alkali metal oxide, e.g. sodium oxide. The alkali metal sulfide is usually contained therein in a major amount and usually in excess of 50 percent by weight, and the alkali metal oxides are present therein in a small amount and usually less than percent by weight. The copper sulfides may be present in this matte phase layer in amount of about -25 percent by weight. This is to be contrasted with the refining slag layer of the prior art which usually contains in excess of 90 percent by weight of alkali metal oxide, e.g. sodium oxide, which is the refining agent as previously set forth herein, and a small, inconsequential amount of sodium sulfide as an impurity only and not as a refining or purifying agent.

The amount of alkali metal sulfide utilized for treating the molten copper in accordance with this invention will depend on the amount of selenium contained in the copper to be de-selenized, and the value or level to which the selenium is to be reduced, and can be varied over quite a broad range so long as there is present an amount of the alkali metal sulfide which is sufficient to lower or reduce the selenium content of the molten copper to the desired value. For reducing the selenium content of molten copper containing about 0.30-0.45 percent by weight Se to a level of below 0.15 percent Se, there will ordinarily be required about 1.5-3 percent by weight of the alkali metal sulfide (calculated as sodium sulfide) based on the molten copper charge.

Although I do not wish to be bound by theory, it appears the de-selenizing of this invention involves the formation of an alkali metal sulfide-selenium complex in the refining matte phase layer and/or dissolution of the selenium in the alkali metal sulfide of the refining matte phase layer.

In the embodiment of the present invention wherein the alkali metal sulfide is formed in situ, i.e. in contact with the molten copper, by addition to the molten copper of an alkali metal sulfate, eg sodium sulfate, and a carbonaceous reducing agent, e.g. coke, a thick, foamy, readily separable or -skimmable refining matte phase layer containing alkali metal sulfide as refining agent is formed on the molten copper surface due to apparently the CO and/or CO evolved by the reaction of the alkali metal sulfate and carbonaceous reducing agent. Now this thick, foamy refining matte phase layer must be retained on the molten copper surface for a time which is sufficient to enable passage of sufficient selenium into the matte phase layer to reduce the selenium content of the copper to the desired low level. However if this matte phase layer is retained on the molten copper surface for too long a time, the thick, foamy, readily-separable matte phase layer initially formed will be converted into a thin, nonfoamy, matte phase layer on the molten copper surface which is of watery consistency, i.e. low viscosity, and difficult to cleanly separate from the molten copper. This is due to escape of the gas, apparently CO and/or CO as aforementioned, from the foam bubbles resulting in the breakdown of the foam. The process of this embodiment of the invention comprises:

a. treating the selenium-containing molten copper with the alkali metal sulfate and the carbonaceous reducing agent, the alkali metal sulfate endothermically reacting with the carbonaceous reducing agent in situ to form an alkali metal sulfide;

b. forming a thick, foamy, readily-separable or skimmable refining matte phase layer containing the alkali metal sulfide as refining agent on the molten copper surface due to the reaction of the alkali metal sulfate and carbonaceous reducing agent;

c. retaining the refining matte phase layer on the molten copper surface for a period sufficient to enable passage of the selenium into said matte phase layer in amount sufficient to reduce the selenium content of the molten copper down to a desired lower level or value, but which is an insufficient time to yield a thin, non-foamy, watery consistency, difficulty-skimmable matte phase layer on the mo]- ten copper surface; and

d. separating the readily-separable matte phase layer containing the selenium from the de-selenized copper.

The specific thickness of the readily-separable or skimmable matte phase layer containing the selenium obtained in accordance with this embodiment of the invention is dependent on the furnace geometry and configuration. Thus with a holding furnace of a geometry and configuration to allow for a deep molten metal bath with a small surface area, the readily-separable or skimmable matte phase layer containing the selenium will usually be of greater thickness than is the case with use of a holding furnace of a geometry and configuration allowing for a shallow bath of molten metal with a relatively large surface area, wherein the readilyseparable or skimmable matte phase layer containing the selenium is usually of lesser thickness. Typically the readily-separable or skimmable matte phase layer con taining the selenium is of a thickness or depth in the range from about two inches to about three inches or greater at the time of separation from the copper by skimming or otherwise.

In the embodiment of this invention set forth supra involving the in situ formation of the alkali metal sulfide by reaction in situ of the alkali metal sulfate and carbonaceous reducing agent, the problem was encountered of loss of heat from the molten copper due to the endothermic reaction between the alkali metal sulfate and the carbon of the carbonaceous reducing agent. This heat loss from the molten copper was quite high and resulted in a large solidified copper accretion in the holding furnace. The presence of this solidified copper accretion in the furnace is disadvantageous for the reason that selenium is trapped in the solidified copper and hence cannot be removed from the copper. Moreover it takes heat and time to melt the solidified accretion.

In accordance with still another embodiment of the invention, the process comprises:

a. heating the copper to be de-selenized to a tempe rature considerably above the melting point of the copper, and usually at least about 30C. above the melting point of copper;

b. treating the selenium-containing molten copper with the alkali metal sulfate and the carbonaceous reducing agent, the alkali metal sulfate endothermically reacting with the carbonaceous reducing agent in situ to form the alkali metal sulfide;

c. forming the thick, foamy, readily-separable orskimmable refining matte phase layer containing the alkali metal sulfide as refining agent on the molten copper surface due to the reaction of the alkali metal sulfate and carbonaceous reducing agent;

d. maintaining the temperature of the molten copper sufficiently elevated to prevent solidification of the copper due to cooling by reason of the endothermic reaction of the alkali metal sulfate and the carbonaceous reducing agent, for instance by introducing sufficient superheat, i.e. heat above the melting point of the copper, into the seleniumcontaining copper as in step (a), to accomplish this;

e. retaining the refining matte phase layer on the molten copper surface for a period sufficient to enable passage of the selenium into the matte phase layer in amount sufficient to reduce the selenium content of the molten copper down to the desired low level or value, but which is insufficient to yield the thin, non-foamy, watery consistency, difficultlyskimmable matte phase layer on the molten copper surface; and

f. separating the readily-separable matte layer containing the selenium from the de-selenized copper.

The temperature of the molten copper can be maintained sufficiently elevated to prevent the cooling and solidification of the copper due to the endothermic reaction of the alkali metal sulfate and the carbonaceous reducing agent by any suitable method or means. For example, one way this can be accomplished is by injecting sufficient superheat, i.e. heat above the melting point of copper, into the molten copper, prior to the addition of the alkali metal sulfate and carbonaceous reducing agent, to accomplish this, for example by the proper adjustment of the burners of the holding furnace to obtain maximum flame temperature. Another way this can be accomplished is by the installation of burners in the furnace capable of supplying a greater amount of heat to the molten copper. Another way this can be accomplished is by treating or adding to each charge of copper in the treatment zone, such as for instance a holding furnace equipped with oil burners, the substantially maximum amount of alkali metal sulfate, e.g. sodium sulfate, and of carbonaceous reducing agent, such as coke, that will not result in cooling the molten copper to a temperature resulting in solidification of the copper and usually that will not result in cooling the molten copper below about 11 15C. by the endothermic reaction, but which reactants are present in sufficient amount for the reaction to form the alkali metal sulfide. When the copper has about 150C. of superheat, i.e. heat above the melting point of copper, such maximum amount of alkali metal sulfate is about 2 A percent by weight (calculated as sodium sulfate) based on the copper charge, and such maximum amount of the coke is about 1 percent by weight based on the copper charge. When sufficient time is available before the next copper charge, the molten copper maintained by heating or otherwise at a temperature sufficiently elevated to prevent cooling solidification of the copper and usually at a temperature of above l1l5C. is treated with another addition of the alkali metal sulfate and carbonaceous reducing agent, in the substantially maximum amount of these materials that will not result in cooling of the molten copper to a temperature resulting in cooling solidification of the molten copper and usually that will not result in cooling the molten copper below lll5C. while reacting to form the alkali metal sulfide, and the resulting refining matte phase layer is retained on the molten copper for a period sufficient to enable passage of the selenium into the matte phase layer but insufficient to yield the thin, nonfoamy, difficultly-separable matte phase layer on the molten copper surface. The thick, foamy, readilyseparable matte phase layer is then separated from the molten copper. This procedure involving treating the molten copper maintained at a temperature of usually above 1 15C. by heating or otherwise with another addition of the alkali metal sulfate and solid carbonaceous reducing agent can be repeated any desired or required number of times.

The alkali metal sulfate utilizable in the process of this invention is exemplified by sodium sulfate, potassium sulfate and lithium sulfate.

The carbonaceous reducing agents utilizable in the instant process are, for example, solid carbonaceous reducing agents, e.g. coke, charcoal and coal. A liquid carbonaceous reducing agent such as a normally liquid petroleum hydrocarbon fraction or oil is also utilizable but is not preferred when added to the surface of the molten copper as it flashes off. A reducing gas such as,

' for example, natural gas, methane or CO is also utilizable as the reducing agent but is not preferred.

The solid carbonaceous reducing agent and alkali metal sulfate are usually added to the surface of the molten copper. However, alternatively these materials may be injected below the surface of the molten copper by being blown in or otherwise introduced through tuyeres in the holding furnace, or these materials can be charged to the bottom of the furnace or other vessel prior to introducing the molten copper therein. The normally liquid petroleum hydrocarbon fraction or reducing gas, where utilized, are usually introduced into the molten copper through the tuyeres.

When the solid carbonaceous reducing agent and alkali metal sulfate are added to the molten copper surface, the carbonaceous reducing agent in finely particulate form and the alkali metal sulfate are usually premixed in a metallic boat or scoop, and the resulting mixture dumped or poured from the boat through an opening in the furnace and onto the molten metal surface.

The sodium sulfide utilized in this invention can be a stoichiometric sodium sulfide, i.e. Na S, or a non-stoichiometric sodium sulfide. Good results were achieved in de-selenizing molten copper in accordance with this invention utilizing a non-stoichiometric sodium sulfide of the formula Na Sx wherein x had a value in the range of 0.9-1 .1. A hydrated sodium sulfide of commerce can be utilized but is not recommended due to an explosion hazard due to the water of hydration.

Any suitable furnace or other suitable vessel can be utilized for retaining the molten copper to be deselenized. The furnace or other vessel, be it a holding furnace, anode furnace, etc. may be equipped with suitable burners such as .oil or gas burners and, if desired, with tuyeres. A furnace equipped with tuyeres is of course required if the carbonaceous reducing agent is to be introduced into the molten metal through the tuyeres.

The copper of reduced selenium content obtained in accordance with any embodiment of this invention may be subjected to blowing for oxidation removal of sulfur in the copper. Subsequent to the blowing, the copper is ordinarily poled to remove the oxygen introduced into the copper during the blowing. ln blowing the molten copper, the oxygen-containing gas, ordinarily air, is injected below the surface of the molten copper pool in the refining furnace, which may be the anode furnace, through one or more pipes, lances or tuyeres having their outlets submerged below the molten copper surface. in oxidizing sulfur in the copper to sulfur dioxide, the oxygen-containing blowing gas also oxidizes a portion of the copper which is dissolved in the molten copper, the blowing being continued until the sulfur in the molten copper is reduced to a desired amount.

The poling of the molten copper to remove unwanted oxygen is effected by introducing a poling agent, for example a green tree, coke or an appropriate poling gas, for example a hydrocarbon gas such as natural gas, beneath the surface of the molten copper, the poling being continued until the oxygen in the copper is reduced to a desired value. The poling gas, likewise may be injected beneath the molten copper surface through one or more lances, pipes or tuyeres having their out lets submerged below the surface of the molten copper pool. For casting the fire-refined copper into anodes, the oxygen content of the blown copper is usually reduced during the poling step to an oxygen content of about 0.05 to 0.1 percent oxygen by weight. However, when the fire-refined copper is to be cast into semifinished shapes, the oxygen content of the copper is reduced during the poling step to a value below 0.05 percent oxygen by weight, usually in the range 0.015 to 0.04 percent oxygen by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred alkali metal sulfide for use herein is an anhydrous or substantially anhydrous alkali metal sulfide. Preferred among the alkali metal sulfides is sodium sulfide.

The preferred alkali metal sulfate is sodium sulfate.

The preferred carbonaceous reducing agent is the solid carbonaceous reducing agent. Coke is preferred among the solid carbonaceous reducing agents.

The molten copper is preferably maintained at a temperature of above llC. during the rocess of this invention.

The molten copper beneath the surface of the molten copper pool is preferably agitated during and/or after treating the selenium-containing molten copper with the alkali metal sulfide added as such or formed in situ as previously disclosed herein. The agitating is a substantial or significant agitation of the molten copper and serves to bring the selenium-containing molten copper beneath the pool surface into intimate contact with the refining matte phase containing the alkali metal sulfide and hence enable the removal of even greater amounts of selenium from the copper. The agitating causes the selenium containingmolten copper beneath the pool surface and in the lower, intermediate and upper portions of the pool to pass or circulate upwardly to the surface of the molten copper whereby the selenium can pass into the refining matte phase. Depending on the vigorousness of the agitating, a portion at least of the refining matte phase layer on the molten pool surface may be broken up and dispersed throughout the molten copper including the copper in the lower and intermediate portions of the pool as well as in the upper portion of the pool beneath the pool surfacev This breaking and dispersal of a portion or all of the refining matte phase through the molten copper in the pool may occur with more vigorous agitating of the pool, and by being dispersed throughout the molten copper, the refining matte phase also comes into intimate contact with the selenium-containing molten copper in the lower, intermediate and upper portions of the pool whereby the selenium passes into the refining matte phase. On discontinuing the agitating, the dispersed refining matte phase containing the selenium soon passes upwardly to the top surface of the melt pool and forms the refining matte phase layer thereon. Additional selenium may pass into the refining matte phase layer after it forms on the pool surface.

The agitating of the molten copper is carried out for a time sufficient to enable the selenium to pass into the refining matte phase. Typically the agitating of the molten copper herein is conducted for a period of about 15-20 minutes.

The agitating is carried out by means of an agitating gas or by suitable mechanical agitating or stirring apparatus. The agitating gas is injected beneath the surface of the molten copper through the tuyeres of a tuyereequipped furnace. Alternatively the agitating gas can be injected into the molten copper beneath the molten copper surface through lances. Any suitable gas is utilizable for the agitating. A reducing gas, e.g. natural gas, a gaseous hydrocarbon, for example propane, or an inert or substantially inert gas, e.g. nitrogen, is preferred for the agitating. The reducing gas is most preferred as between the reducing gas and inert gas. Although not preferred, even an oxygen-containing gas such as air can be utilized as the agitating gas but in this event poling is required after the selenium removal treatment. Electromagnetic agitating of the molten copper is also utilizable herein. Rocking or tilting of the tiltable anode furnace or other furnace back and forth to agitate the molten copper therein can also be employed but is not preferred. The molten copper can also be agitated by immersing wood poles or green trees in the melt pool and chaining or otherwise securing the poles or trees beneath pool surfaces. The gases evolved from the wood by the heat of the molten copper and which include CO, H and water vapor pass upwardly through the melt and agitate the molten copper. Agitating of the molten copper beneath the melt surface can also be carried out herein by mean of the CO and/or CO gas evolved during the in situ formation of the alkali metal sulfide by the reaction between the alkali metal sulfate and the carbonaceous reducing agent, for instance coke. When agitation by such gas is desired, the alkali metal sulfate and coke is placed on the furnace or vessel bottom and the selenium-containing molten copper poured onto these reactants. The evolved gas due to the reaction between the alkali metal sulfate and coke passes upwardly in the molten copper and agitates the molten copper beneath the melt surface, which causes upward movement of the selenium to the melt surface where the selenium can pass into the refining matte phase layer.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a view, diagrammatic in nature, howing a furnace for practicing the invention; and

FIG. 2 is an enlarged sectional view of a tuyere taken on line 2-2 of FIG. 1.

Referring to FlG.s 1 and 2, the furnace l is a conven tional furnace provided with a pair of tuyeres 2, burner 3, flue 4 having conventionally mounted damper 5,

pouring spout 7, skim port 8 and charge port 9. The furnace is conventionally mounted on rollers by means of collars and rollers 11 and is provided with conventional drive means (not shown) for rotating the furnace. Thus, for example, the furnace can be rotated from its normal operating position shown in FIG. 1 to a position to pour metal through the pouring spout 7 or it can be rotated to elevate the outlets of the tuyeres to a position above the level of the metal in the furnace. Likewise it can be rotated to move ports 8 and 9 into more convenient positions.

Any number of tuyeres may be provided for the furnace; the number provided being dependent on the rate at which agitating gas or the poling gas is to be injected into the furnace. As shown, furnace 1 is provided with two tuyeres 2 disposed at a distance from the ends of the furnace of about one-third the length of the furnace. Where additional tuyeres are used, the tuyeres preferably are mounted to be spaced uniformly along the length of the furnace. As shown in FIG. 2 the tuyeres 2 include a tuyere pipe extending through plate 16 and furnace lining 17. Plate 16 is suitably secured, as by bolts 18 to the metal shell 19 of the furnace. Tee 21 is threaded onto tuyere pipe 15. Threaded into one end of tee 21 is pipe 22 provided with valve 23. Flexible air hose 24 is attached to pipe 22 for delivering air through the tuyere into the furnace. Pipe 30, provided with valve 31, is threaded into the other end of the tee. The end of pipe 30 away from the tee is connected to flexible conduit 32 for feeding agitating gas, e.g. natural gas, or poling gas (from a source not shown) through the tuyere into the furnace. The top, bottom, side and end walls of the furnace are conventionally lined with lining 17, shown in FIG. 2, which is comprised of an innermost layer of magnesite brick 35 and a layer of suitable insulating material 36, between the brick and shell 19. Tees 21 may also be provided with a conventional tuyere punching opening aligned with pipe 15 for insertion of a conventional tuyere punching tool.

In operation, an alkali metal sulfide, e.g. sodium sulfide, is supplied onto the surface of the seleniumcontaining molten copper, e.g. blister copper, in furnace 1 through charge port 9. The sodium sulfide had previously been heated in a furnace to expel all or virtually all of the water from the sodium sulfide. A refining matte phase layer forms and floats on top of the molten copper. With valves 23 in pipes 22 closed and valves 31 in pipe 30 open and furnace 1 rotated to lower the outlets of tuyere pipes 15 typically 18 inches below the molten copper pool surface, an agitating gas, e.g. natural gas or a gaseous hydrocarbon, for example propane, is fed at a predetermined or positive pressure of typically about 15-30 psig and supply rate of typically 5,000-10,000 standard cubic feet of gas per hour, which are sufficient to agitate the molten copper the desired extent, from a source of such gas (not shown) through flexible conduits 32, pipes 30, tees 21 and tuyere pipes 15 and injected beneath the surface of the molten copper in furnace 1, whereby the molten copper is agitated. Due to this agitation of the molten copper, selenium-containing molten copper in the intermediate and lower portions of the molten copper pool in the furnace 1 as well as in the upper portion but beneath the top surface of the molten copper pool is brought into intimate contact with the refining matte of the copper pool where it is subjected to the action of the refining matte phase, usually by being caused to pass or move upwardly into contact with the refining matte phase layer floating on the surface of the molten copper pool whereby the selenium passes into the refining matte phase and is removed from the copper. The agitation is continued for a period of typically 15-20 minutes.

The refining matte phase layer is retained on the surface of the molten copper in furnace 1 for a period, typically about 30 minutes, which is sufficient to enable passage of a sufficient amount of selenium into the matte phase layer to reduce the selenium content of the molten copper to the desired value. The refining matte phase layer and hence the selenium are then separated from the molten copper by skimming off the refining matte layer and selenium through skim port 8. Prior to the skimming, the furnace 1 is rotated to raise the outlets of the tuyere pipes 15 as well as skim port 8 above the level of the molten metal 40 and the tuyere pipe outlets are then closed by mudding with a suitable refractory material, e.g. fire clay. The furnace 1 is then rotated to lower skim port 8 to about the level shown in FIG. 1 herein and to lower the closed tuyere pipe outlets to about their former level below the level of the molten metal 40.

The copper of reduced selenium content may then be subjected to blowing for oxidation removal of any sulfur therein introduced by the alkali metal sulfide. Prior to the blowing, the furnace 1 is rotated to raise the outlets of the tuyere pipes 15 above the level of the molten metal and these tuyere pipe outlets are opened by removal of the refractory material therefrom. The furnace is then rotated to lower the open tuyere pipe outlets to below the surface of the molten metal. The free oxygen-containing gas, ordinarily air, is fed at a positive pressure through hose 24, pipe 22, tee 21 and tuyere pipe 15 and injected beneath the surface of the molten copper pool in furnace 1. The oxygen-containing gas is injected beneath the molten copper surface at a predetermined or desired positive pressure and rate sufficient to remove or reduce the sulfur from the copper to the desired amount. After the blowing step is finished, the slag may be skimmed from the molten copper surface. p

The copper in furnace l is then poled to remove unwanted oxygen. Prior to the poling, furnace l is rotated to elevate the outlets from tuyere pipes 15 above the level of the pool of molten metal 40, spout 7 having been previously suitably plugged with clay. While passing a poling gas, for example natural gas, through hose 24, pipe 30, tee 21 and tuyere pipe 15, which tuyere elements are also utilizable for injecting agitating gas beneath the molten copper surface as is previously disclosed herein, ports 8 and 9 are suitably closed with a suitable refractory material, for example fire clay, or by door members which may be sealed about their edges with the refractory material. If no heat is to be added during the poling step, the inlet for the burner may be closed with the refractory material and the damper may also be closed. With the furnace thus readied, it is rotated to submerge the outlets of tuyere pipes 15 typically 18 inches beneath the molten copper surface, and the natural gas is introduced at a predetermined positive pressure and rate beneath the surface of the molten copper pool. This introduction of the natural gas beneath the surface of the molten copper is continued until the oxygen content of the copper is reduced to a desired value.

The selenium-containing refining mattes produced and separated by this invention can be stockpiled for tervals. Occasionally the matte phase was removed from the bath at the completion of a test by allowing it to freeze to a cold graphite rod. Coppers high thermal conductivity prevented its solidification and adherence selenium recovery. Alternatively the mattes can be 5 to the graphite. treated immediately or substantially immediately or Tests in the induction furnace were run in a similar after separation from the copper without stockpiling of manner. In these tests the surface of the matte was consuch matte for recovery of selenium. tinually exposed to air. Copper on melt down was also Tests were carried out in silicon carbide crucibles exposed to oxidation. At the completion of the tests in held in a natural gas fired pot furnace. Temperatures the induction unit, the contents of the test crucible were measured in these tests with an optical pyrometer. were always cast into an empty graphite crucible to Additional tests were run in an induction furnace. preserve the cermet sleeve for reuse. These additional tests used clay-graphite crucibles Prior to the tests a supply of crude anhydrous sodium which were machined to accept a cermet sleeve that sulfide was prepared by heating a commercial hydrated was placed in the crucible on its upper portion so that flake sodium sulfide under a reducing atmosphere until the matte phase would not contact the clay-graphite no further water was evolved. The results are set forth crucible during a test, but would contact a cermet in the table which follows:

Refined Refining Head Cu copper matte Extraction Example percent PCTCCHK percent percent percent Number Se Reagent C. Se Se Se 1 0.37 4.5 N225 1100 0.004 4.5 99 2... .15 3.0 Nags 1100 .004 1.54 97.5 3... .07 3.8 N325 1130 .002 1.1 97 4... .070 2.1 NaZS i120 .004 1.3 94.5

5... .06 4 K S, 1160 .012 0.91 80 6... .046 2 Net- 50 l Coke 1120 .0046 3.2 89

7... .0005 2 Na; 1160 .0001 .007 8... .06 4 K230i, 2 Coke. 1120 .0028 .90 96.5 9... .058 l was 1200 .034 .16 41 l .28 2 N225 1160 .088 4.04 68 l .14 lN'a S 1200 .082 .22 43 1- .052 2 was 1320 .003 .88 95 l .06 4CaS 1175 .06 0 14... .21 4Na- SW. 1155 .0033 2.1 98.5 15... .30 1 Mrs... H50 .058 7.9 81 16.. .054 4 Na sO 1140 .0007 1.1 99 17 .050 4 Na SO; 1150 .0003 99 I8... .057 4 T 32504 1250 .0002 +99 19 .045 4 192. 50 1350 .0035 92 sleeve instead. This was done to prevent undesirable As is shown by the test results of the table, excellent rematte-crucible reactions. In several of these tests tem- 45 movals or extractions of Se from the molten copper peratures were measured with a chromel-alumel therwere attained using the alkali metal sulfide and also the mocouple. Several tests were run using samples of alkali metal sulfate plus coke. Examples No.s 9, l0 and anode copper. in other tests scrap pieces of wire bar 11 of the foregoing table were the tests carried out in copper were used. In these last-mentioned tests the the induction furnace. The K 8, reagent in Example molten copper was intentionally doped with Se addi- No. 5 of the table was a non-stoichiometric potassium tions. Alloys of Se and copper were used for this doping in early tests. Subsequently it was found the elemental shot containing Se could be added directly to the molten copper with only minor volatilization loss.

For a standard test a known weight of Cu was placed in the crucible and melted. The atmosphere in the laboratory furnace was maintained reducing. Once molten, doping additions were made to the copper. The copper was often, but not always, poled at this point with a wood dowel to provide deoxidation. Samples of the head copper were removed from the molten copper bath at predetermined time intervals. Once the system was stabilized at the desired operating temperature, 1l50C. for most tests, either anhydrous sodium sulfide per se, sodium sulfate and coke, or other reagents were introduced onto the molten copper bath. Additional copper samples were taken at predetermined time insulfide wherein x had a value in the range of 0.9-1.1. The following additional examples further illustrate the invention:

EXAMPLE 20 which was sufficient to enable a considerable amount of the selenium to pass into the matte phase layer but insufficient to yield a thin, non-foamy, difficultyskimmable matte phase layer on the molten copper. Instead this foamy matte phase layer had only partially subsided to a depth of about three inches after the 30 minute retention period and was still fairly thick and readily-skimmable and was readily and cleanly skimmed from the molten copper. The copper was sampled and found to contain 0.26 percent Se. The temperature of the molten copper was above 1100C.

The thus-obtained copper containing 0.26 percent Se was reheated in the furnace to a temperature of 1215C. A second batch of the refining reagents consisting of 600 kilograms of anhydrous sodium sulfate and 250 kilograms of metallurgical coke was placed on the molten copper surface. These reagents reacted endothermically and vigorously to form a thick, foamy, readily-skimmable matte phase layer on the molten copper surface which initially was about six inches thick or deep. The matte phase layer was retained on the molten copper surface for 30 minutes which was sufficient to enable passage of a considerable amount of the residual selenium into the matte phase layer but insufficient to yield a thin, non-foamy, watery, difficulty-skimmable matte phase layer on the molten copper. The matte phase layer had only subsided to a thickness of about three inches after the 30 minute retention period and was readily and cleanly skimmed from the copper. The thus-treated copper was sampled and found to contain only 0.15 percent Se. Such copper was at a temperature of 1110C. Selenium was recovered from both refining mattes.

EXAMPLE 21 Twenty-one metric tons of molten copper containing 0.30 percent Se was heated in a furnace fired with oil burners to 1225C. 600 kilograms of anhydrous sodium sulfate and 250 kilograms of metallurgical coke were added onto the surface of the molten copper. The sodium sulfate and coke reacted endothermically and vigorously to form a thick, foamy, readily-skimmable refining matte phase layer initially about six inches thick or deep on the molten copper surface. This matte phase layer was retained on the molten copper for 30 minutes which was sufficient to enable a considerable amount of the selenium to pass into the matte phase layer but insufficient to yield a thin, non-foamy, difficultyskimmable matte phase layer on the molten copper. The foamy matte phase layer had only partially subsided to a depth of about three inches after the 30 minutes retention period and was readily and cleanly skimmed from the molten copper. The copper was sampled and found to contain 0.16 percent Se. The temperature of the molten copper was 1150C.

The thus-treated copper containing 0.16 percent Se was reheated to 1215C. The second batch of refining agents consisting of 600 kilograms of anhydrous sodium sulfate and 250 kilograms of coke was placed on the molten copper surface. These reagents reacted endothermically and vigorously to form a thick, foamy, readily-skimmable matte phase layer on the molten copper surface which initially was about five inches thick or deep. The matte phase layer was retained on the molten copper for 30 minutes which was sufficient to enable passage of a major portion of the residual selenium into the matte phase layer but insufficient to yield a thin, non-foamy, watery, difficulty-skimmable matte phase layer on the molten copper. The matte phase layer had only subsided to a thickness of about three inches after the 30 minute retention period and was readily and cleanly skimmed from the copper. The thus-treated copper was sampled and found to contain only 0.07% Se. This copper was at a temperature of 1110C. Selenium was recovered from both refining mattes.

EXAMPLE 22 Seventeen metric tons of copper containing 0.43% Se was heated to 1230C. in a holding furnace fired with oil burners. 600 kilograms of anhydrous sodium sulfate and 250 kilograms of coke were placed on the surface of the molten copper. The sodium sulfate and coke reacted vigorously and endothermically to form a thick, foamy, readily-skimmable matte phase layer initially about six inches thick or deep on the molten copper surface. After the matte phase layer had been retained on the molten copper for 30 minutes, during which a considerable amount of the selenium passed into the matte phase layer, this matte phase layer, which was still about three inches thick or deep and foamy, was readily and cleanly skimmed from the molten copper. The copper was sampled and found to contain 0.23% Se.

The thus-obtained copper was reheated in the furnace to a temperature of 1 190C. 400 kilograms of anhydrous sodium sulfate and kilograms of coke were introduced onto the molten copper surface. These reagents reacted vigorously and endothermically to form a thick, foamy, readily-skimmable refining matte phase layer initially about five inches deep on the molten copper surface. After a retention time of 30 minutes of the matte phase layer on the molten copper, during which a considerable amount of the residual selenium passed into the matte phase layer, this matte phase layer, which was still about 2 7% inches thick or deep, was readily and cleanly skimmed from the molten copper surface. Analysis of a sample of the copper showed the copper to contain 0.1 1% Se. The copper was at a temperature of 1140C.

EXAMPLE 23 One thousand one hundred and eighty kilograms of hydrated sodium sulfide containing 40 percent water was charged to an empty holding furnace fired with oil burners. This material was heated to a temperature of 1 150C. at which point all of the water had been eliminated from the sodium sulfide. 22 metric tons of copper containing 0.33% Se was then charged into the furnace. A refining matte phase layer floated on top of the copper. 30 minutes after completion of the copper charging, during which time a major portion of the Se passed into the matte phase layer, the matte phase layer was skimmed from the copper surface. The copper was sampled and found to contain 0.08% Se. The temperature of the copper was 1115C. Selenium was recovered from the refining matte.

EXAMPLE 24 Four-hundred and six short tons of copper containing 0.11% Se was melted in a commercial anode furnace. The molten copper was heated to 1 120C. 7.2 tons of anhydrous sodium sulfate and 2.25 tons of coke breeze were placed on the molten copper surface. A vigorous endothermic reaction occurred between the sodium sulfate and coke to result in a thick, foamy, readilyskimmable refining matte phase layer initially of about four inches in thickness or depth being formed on the molten copper surface. This matte phase layer was not removed from the molten copper until 1 5). hours after addition of the sodium sulfate and coke breeze. At this time the matte phase layer was a very thin, non-foamy, low viscosity layer of only about 1% inch in thickness and which was difficult and time consuming to skim from the copper. The temperature of the copper was below llC. After the skimming removal of the matte phase layer was completed, an undesirable build up of solidified metal was detected on the bottom of the furnace. The thus-treated copper was sampled and found to contain 0.064% Se. The selenium was recovered from the refining matte.

EXAMPLE 25 Twentytwo metric tons of copper containing 0.33% Se is heated to lllC. in a tilting horizontal furnace equipped with two spaced-apart tuyeres in the furnace side wall for introducing gas beneath the surface of the pool of molten copper therein. 800 kilograms of anhydrous sodium sulfide is placed on the surface of the molten copper. The sodium sulfide is heated in a sepa rate furnace to a temperature of ll50C. to eliminate all of the water therefrom prior to being placed on the molten copper surface in the first-mentioned furnace. A refining matte phase layer containing the sodium sulfide forms after a few minutes and floats on the molten copper pool. Natural gas as agitating gas is then in jected into the pool of molten copper and beneath its pool surface through the tuyeres. The natural gas is injected into the molten copper pool at a pressure of 20 psig and a flow rate of 10,000 standard cubic feet of gas per hour to agitate the molten copper and to circulate the molten copper in the lower, intermediate and upper portions of the pool upwardly and into contact with the refining matte phase layer containing the sodium sulfide floating on the pool top surface. The molten copper in the pool is agitated by means of the injected agitating gas for about 20 minutes, after which the agitation is discontinued. After an additional minutes, the refining matte phase layer is skimmed from the cop per surface. The copper is sampled and found to contain 0.05% Se. Selenium is recovered from the refining matte.

EXAMPLE 26 Twenty-two metric tons of copper containing 0.35% Se is heated to ll25C. in a tilting horizontal furnace equipped with two spaced-apart tuyeres in the furnace side wall for introducing gas beneath the surface of the molten copper pool therein. 780 kilograms of anhydrous sodium sulfide is placed on the surface of the molten copper. Prior to being placed on the molten copper surface, the sodium sulfide is heated in a separate furnace to a temperature of 1150C. to eliminate the water therefrom. A refining matte phase layer containing sodium sulfide forms after a few minutes and floats on the molten copper pool. Propane gas as agitating gas is then injected into the pool of molten copper and beneath its surface through the tuyeres. The propane is injected into the molten copper pool at a pressure of 25 psig and a flow rate of 8,000 standard cubic feet of gas per hour, to agitate the molten copper and to circulate the molten copper in the lower, intermediate and upper portions of the pool upwardly and into contact with the refining matte phase layer containing the sodium sulfide floating on the pool top surface. The molten copper in the pool is agitated by means of the injected propane gas for about 20 minutes, after which the agitating is discontinued. After an additional 10 minutes, the refining matte phase layer is skimmed from the copper pool surface. The copper is sampled and found to contain 0.06% Se. Selenium is recovered from the refining matte.

What is claimed is:

l. A process for the removal of selenium from molten copper, which comprises:

a. treating the molten copper containing selenium with an alkali metal sulfide by adding the alkali metal sulfide per se to said molten copper;

b. forming a refining sulfide matte phase containing a refining agent of which the alkali metal sulfide is the major refining constituent in contact with the molten copper as a result of the alkali metal sulfide treatment;

c. maintaining the refining matte phase in contact with the molten copper for a period sufficient to enable passage of a sufficient amount of selenium into the refining matte phase to reduce the selenium content of the copper to a desired value; and

d. separating the selenium in the refining matte phase from the molten copper while said matte phase is on the molten copper surface as a refining matte phase layer.

2. A process for the removal of selenium from molten copper, which comprises:

a. treating the molten copper containing selenium with an alkali metal sulfide by adding the alkali metal sulfide per se to said molten copper;

b. forming a refining sulfide matte phase layer containing a refining agent of which the alkali metal sulfide is the major refining constituent on the molten copper surface as a result of the alkali metal sulfide treatment;

c. retaining the matte phase layer on the molten copper surface for a period sufficient to enable passage of a sufficient amount of selenium into the matte phase layer to reduce the selenium content of the copper to a desired value; and

d. separating the selenium in the matte phase layer from the molten copper.

3. The process of claim 2 wherein the alkali metal sulfide is a substantially anhydrous alkali metal sulfide.

4. The process of claim 2 wherein the selenium in the matte phase layer is separated from the molten copper by skimming the matte phase layer.

5. The process of claim 2 wherein the thus-obtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.

6. The process of claim 2 wherein the seleniumcontaining molten copper treated is blister copper.

7. The process of claim 2 wherein the seleniumcontaining molten copper beneath the molten copper surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.

8. The process of claim 7 wherein the agitating is carried out by means of an agitating gas injected beneath the molten copper surface.

9. The process of claim 8 wherein the agitating gas is injected beneath the molten copper surface through the tuyeres of a tuyere-equipped furnace.

10. The process of claim 8 wherein the agitating gas is a reducing gas.

11. The process of claim 8 wherein the agitating gas is natural gas.

12. A process for the removal of selenium from molten copper, which comprises:

a. treating the selenium-containing molten copper with an alkali metal sulfate and a carbonaceous reducing agent, the alkali metal sulfate endothermically reacting with the carbonaceous reducing agent in situ to form an alkali metal sulfide;

b. forming a thick, foamy, readily separable refining matte phase layer containing the alkali metal sulfide as refining agent on the molten copper surface due to the reaction of the alkali metal sulfate and the carbonaceous reducing agent;

c. retaining the refining matte phase layer on the molten copper surface for a period sufficient to enable passage of the selenium into said matte phase layer but insufficient to yield a thin, non-foamy, difficultly-separable matte phase layer on the molten copper surface; and

d. separating the readily separable matte phase layer containing the selenium from the molten copper.

13. The process of claim 12 wherein the refining matte phase layer is retained on the molten copper surface for a period of at least about 30 minutes but insufficient to yield a thin, non-foamy, difficultly separable matte phase layer on the molten copper surface.

14. The process of claim 13 wherein the matte phase layer is retained on the molten copper surface for a period in the range of about 30-60 minutes.

15. The process of claim 13 wherein the seleniumcontaing matte phase layer is of a thickness in the range from about two to about three inches at the time of separation from the molten copper.

16. The process of claim 12 wherein the seleniumcontaining molten copper treated is blister copper.

17. The process of claim 12 wherein the seleniumcontaining molten copper beneath the molten copper surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.

18. The process of claim 17 wherein the agitating is carried out by means of an agitating gas injected beneath the molten copper surface.

19. The process of claim 18 wherein the agitating gas is injected beneath the molten copper surface through the tuyeres of a tuyere-equipped furnace.

20. The process of claim 19 wherein the agitating gas is a reducing gas.

21. The process of claim 20 wherein the agitating gas is natural gas.

22. The process of claim 12 wherein the thusobtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.

23. The process of claim 12 wherein the temperature of the molten copper is maintained sufficiently elevated to prevent solidification of the copper due to cooling thereof by reason of the endothermic reaction of the alkali metal sulfate and carbonaceous reducing agent.

24. The process of claim 23 wherein the seleniumcontaining molten copper treated is blister copper.

25. The process of claim 23 wherein the temperature of the molten copper is maintained sufficiently elevated to prevent the cooling solidification of the copper by introducing sufficient superheat into the molten copper prior to adding the alkali metal sulfate and carbonaceous reducing agent thereto.

26. The process of claim 23 wherein the temperature of the molten copper is maintained above lll5C.

27. The process of claim 26 wherein the molten copper temperature is maintained above 1 l 15C. by treating the selenium-containing molten copper with the substantially maximum quantity of the alkali metal sulfate and solid carbonaceous reducing agent that will not result in cooling the copper below lll5C.

28. The process of claim 27 wherein the alkali metal sulfate is sodium sulfate and the carbonaceous reducing agent is coke.

29. The process of claim 23 wherein the seleniumcontaining molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.

30. The process of claim 25! wherein the agitating is effected by means of an agitating gas injected beneath the molten copper surface.

31. The process of claim 27 wherein after separating the refining matte phase layer containing the selenium from the copper, the molten copper at a temperature of above 1 l 15C. is treated with another addition of the alkali metal sulfate and carbonaceous fuel reducing agent, followed by the retention of the refining matte phase layer on the molten copper for a period sufficient to enable passage of the selenium into the refining matte phase layer but insufficient to yield a thin, nonfoamy, difficulty separable matte phase layer on the molten copper surface, and separation of the readily separable matte phase layer from the molten copper.

32. The process of claim 31 wherein the procedure is repeated at desired number of times.

33. The process of claim 23 wherein the thusobtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.

34. The process of claim 31 wherein the seleniumcontaining molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.

35. The process of claim 32 wherein the seleniumcontaining molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.

g gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,772,001 Dated November 13, 1973 Inventor-(s) Harold L r n It is certified that error appears in the above-identified" patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 13, "affect" should read effect Column 5 line 19, phase should be inserted after "matte" and before "layer", Column 6, line 7, "115C." should ,read M lll5C. Column 8, line 61, "howing should read showing Signed and sealed this 23rd day of April 1971],.

(SEAL) Attest:

EDWARD I-I.FLETCHSR,5Z9 C MARSHALL DANN I Atts sting Officer Commissioner of Patents 

2. A process for the removal of selenium from molten copper, which comprises: a. treating the molten copper containing selenium with an alkali metal sulfide by adding the alkali metal sulfide per se to said molten copper; b. forming a refining sulfide matte phase layer containing a refining agent of which the alkali metal sulfide is the major refining constituent on the molten copper surface as a result of the alkali metal sulfide treatment; c. retaining the matte phase layer on the molten copper surface for a period sufficient to enable passage of a sufficient amount of selenium into the matte phase layer to reduce the selenium content of the copper to a desired value; and d. separating the selenium in the matte phase layer from the molten copper.
 3. The process of claim 2 wherein the alkali metal sulfide is a substantially anhydrous alkali metal sulfide.
 4. The process of claim 2 wherein the selenium in the matte phase layer is separated from the molten copper by skimming the matte phase layer.
 5. The process of claim 2 wherein the thus-obtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.
 6. The process of claim 2 wherein the selenium-containing molten copper treated is blister copper.
 7. The process of claim 2 wherein the selenium-containing molten copper beneath the molten copper surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.
 8. The process of claim 7 wherein the agitating is carried out by means of an agitating gas injected beneath the molten copper surface.
 9. The process of claim 8 wherein the agitating gas is injected beneath the molten copper surface through the tuyeres of a tuyere-equipped furnace.
 10. The process of claim 8 wherein the agitating gas is a reducing gas.
 11. The process of claim 8 wherein the agitating gas is natural gas.
 12. A process for the removal of selenium from molten copper, which comprises: a. treating the selenium-containing molten copper with an alkali metal sulfate and a carbonaceous reducing agent, the alkali metal sulfate endothermically reacting with the carbonaceous reducing agent in situ to form an alkali metal sulfide; b. forming a thick, foamy, readily separable refining matte phase layer containing the alkali metal sulfide as refining agent on the molten copper surface due to the reaction of the alkali metal sulfate and the carbonaceous reducing agent; c. retaining the refining matte phase layer on the molten copper surface for a period sufficient to enable passage of the selenium into said matte phase layer but insufficient to yield a thin, non-foamy, difficultly-separable matte phase layer on the molten copper surface; and d. separating the readily separable matte phase layer containing the selenium from the molten copper.
 13. The process of claim 12 wherein the refining matte phase layer is retained on the molten copper surface for a period of at least about 30 minutes but insufficient to yield a thin, non-foamy, difficultly separable matte phase layer on the molten copper surface.
 14. The process of claim 13 wherein the matte phase layer is retained on the molten copper surface for a period in the range of about 30-60 minutes.
 15. The process of claim 13 wherein the selenium-containg matte phase layer is of a thickness in the range from about two to about three inches at the time of separation from the molten copper.
 16. The process of claim 12 wherein the selenium-containing molten copper treated is blister copper.
 17. The process of claim 12 wherein the selenium-containing molten copper beneath the molten copper surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.
 18. The process of claim 17 wherein the agitating is carried out by means of an agitating gas injected Beneath the molten copper surface.
 19. The process of claim 18 wherein the agitating gas is injected beneath the molten copper surface through the tuyeres of a tuyere-equipped furnace.
 20. The process of claim 19 wherein the agitating gas is a reducing gas.
 21. The process of claim 20 wherein the agitating gas is natural gas.
 22. The process of claim 12 wherein the thus-obtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.
 23. The process of claim 12 wherein the temperature of the molten copper is maintained sufficiently elevated to prevent solidification of the copper due to cooling thereof by reason of the endothermic reaction of the alkali metal sulfate and carbonaceous reducing agent.
 24. The process of claim 23 wherein the selenium-containing molten copper treated is blister copper.
 25. The process of claim 23 wherein the temperature of the molten copper is maintained sufficiently elevated to prevent the cooling solidification of the copper by introducing sufficient superheat into the molten copper prior to adding the alkali metal sulfate and carbonaceous reducing agent thereto.
 26. The process of claim 23 wherein the temperature of the molten copper is maintained above 1115*C.
 27. The process of claim 26 wherein the molten copper temperature is maintained above 1115*C. by treating the selenium-containing molten copper with the substantially maximum quantity of the alkali metal sulfate and solid carbonaceous reducing agent that will not result in cooling the copper below 1115*C.
 28. The process of claim 27 wherein the alkali metal sulfate is sodium sulfate and the carbonaceous reducing agent is coke.
 29. The process of claim 23 wherein the selenium-containing molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.
 30. The process of claim 29 wherein the agitating is effected by means of an agitating gas injected beneath the molten copper surface.
 31. The process of claim 27 wherein after separating the refining matte phase layer containing the selenium from the copper, the molten copper at a temperature of above 1115*C. is treated with another addition of the alkali metal sulfate and carbonaceous fuel reducing agent, followed by the retention of the refining matte phase layer on the molten copper for a period sufficient to enable passage of the selenium into the refining matte phase layer but insufficient to yield a thin, non-foamy, difficulty separable matte phase layer on the molten copper surface, and separation of the readily separable matte phase layer from the molten copper.
 32. The process of claim 31 wherein the procedure is repeated a desired number of times.
 33. The process of claim 23 wherein the thus-obtained de-selenized molten copper is subjected to blowing, and subsequently the molten copper is poled.
 34. The process of claim 31 wherein the selenium-containing molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase.
 35. The process of claim 32 wherein the selenium-containing molten copper beneath the molten metal surface is agitated to bring the selenium-containing molten copper in intimate contact with the refining matte phase. 